Former UFC welterweight champion Georges St-Pierre told reporters in Montreal on Tuesday that the promotion's stance on drug testing contributed to his decision to vacate the title and step away from the sport last month.

Speaking in French, St-Pierre questioned what he perceived to be a lack of support from the UFC in his recent effort to involve the Voluntary Anti-Doping Association in the drug testing of a title fight against Johny Hendricks at UFC 167 in Las Vegas in November.

"It bothered me greatly," St-Pierre said, according to the Canadian Press. "It was one of the reasons I decided to step aside.

"I tried to change things and unfortunately - maybe for money reasons, maybe for image - they were not ready to do that. I tried in a very diplomatic way and it didn't work, so it's unfortunate, but I believe it will happen sooner or later."

Prior to the Hendricks fight on November 16, the 32-year-old St-Pierre confirmed his participation in a voluntary program under VADA and invited his opponent to do the same. Hendricks eventually baulked at the idea, when his management team learned VADA intended to foot the bill, as opposed to it coming out of St-Pierre's pocket. Hendricks didn't trust the relationship between St-Pierre and VADA, but still underwent drug testing performed by the Nevada State Athletic Commission.

Both fighters passed all the tests they were given, and neither ever has tested positive for performance-enhancing drugs.

St-Pierre announced his hiatus one month later, citing a growing level of stress as the primary reason.

UFC CEO and co-owner Lorenzo Fertitta told ESPN on Tuesday that he was "shocked" by St-Pierre's comments. He said the topic of drug testing did not surface when the Canadian star informed the promotion he was vacating the title in December.

"We've made it clear, through presentations at various athletic commissions, that we advocate for the most rigorous drug testing possible," Fertitta said. "We've actually advocated for harsher penalties for PEDs.

"Maybe Georges didn't understand the level of drug testing Nevada was doing. They are the ultimate authority that handles drug testing, medicals and everything else - and they are very capable."

Fertitta said the UFC never have turned down a request from an athletic commission to pay for additional drug testing. That situation occurred last month at UFC 168 in Las Vegas, involving a heavyweight fight between Travis Browne and Josh Barnett. As a requirement to license Barnett, who previously has tested positive for steroids, the NSAC implemented an enhanced, out-of-competition program, which the UFC paid for, according to NSAC executive director Keith Kizer.

Fertitta pointed out that when the promotion is forced to self-regulate, in countries where an athletic commission is absent, it tests every fighter on the card. All UFC athletes are "rigorously" tested before signing their initial contract, as well.

During his comments in Montreal, St-Pierre reportedly referred to the UFC as a "monopoly," and said that might prevent other fighters from speaking publicly about the PED problem in MMA. Fertitta acknowledged an existence of PED use within the UFC, but said the promotion is doing what it can to eliminate it.

"Obviously, we know there are some athletes that do cheat, but we are catching them," Fertitta said. "Hopefully, because the penalties for being caught have gone to the extent they have - monetary, suspensions, revocations of licenses - it's convincing these guys it's not worth it."

St-Pierre (25-2) is one of the most dominant champions in UFC history. He first won the 170-pound title in November 2006 against Matt Hughes. He has still not ruled out an eventual return to the Octagon.